One form of an infrared optical system includes several lenses made of infrared-transparent lens materials such as germanium or silicon. The lenses are arranged at the proper positions along an optical path to achieve the desired effects. However, the refractive index and other optical properties of such infrared lens materials are strongly dependent upon temperature. If the temperature changes so that the optical properties of the lens materials change, the lenses may no longer be properly positioned relative to each other, and the performance of the infrared optical system is degraded.
One approach to reducing the adverse effects of the temperature dependence of the lens properties is to mount one or more of the lenses in a temperature compensator. The axial position of the mounted lens along the optical path is altered by the temperature compensator as the temperature changes, so as to null the effects of the changes in the optical properties of the lens material. In some applications, it is sufficient to mount only the lens having the greatest temperature dependence of its optical properties on the temperature compensator.
This approach works well in applications involving only static forces applied to move the lens mounted on the temperature compensator. However, where the system is subject to vibrations or sudden accelerations, the inventor has observed, in the work leading to the present invention, that the temperature compensator is prone to premature mechanical failure, which in turn leads to a degradation in the properties of the optical system because it can no longer compensate for the changes in the optical properties of the lenses.
There is a need for an improved approach to temperature-compensated optical systems to overcome the sensitivity to vibrations and accelerations. The present invention fulfills this need, and further provides related advantages.